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  <div class="section" id="module-io">
<span id="io-core-tools-for-working-with-streams"></span><h1>16.2. <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> --- Core tools for working with streams<a class="headerlink" href="#module-io" title="永久链接至标题">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/io.py">Lib/io.py</a></p>
<hr class="docutils" />
<div class="section" id="overview">
<span id="io-overview"></span><h2>16.2.1. Overview<a class="headerlink" href="#overview" title="永久链接至标题">¶</a></h2>
<p id="index-0">The <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module provides Python's main facilities for dealing with various
types of I/O.  There are three main types of I/O: <em>text I/O</em>, <em>binary I/O</em>
and <em>raw I/O</em>.  These are generic categories, and various backing stores can
be used for each of them.  A concrete object belonging to any of these
categories is called a <a class="reference internal" href="../glossary.html#term-file-object"><span class="xref std std-term">file object</span></a>.  Other common terms are <em>stream</em>
and <em>file-like object</em>.</p>
<p>Independently of its category, each concrete stream object will also have
various capabilities: it can be read-only, write-only, or read-write. It can
also allow arbitrary random access (seeking forwards or backwards to any
location), or only sequential access (for example in the case of a socket or
pipe).</p>
<p>All streams are careful about the type of data you give to them.  For example
giving a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> object to the <code class="docutils literal notranslate"><span class="pre">write()</span></code> method of a binary stream
will raise a <code class="docutils literal notranslate"><span class="pre">TypeError</span></code>.  So will giving a <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> object to the
<code class="docutils literal notranslate"><span class="pre">write()</span></code> method of a text stream.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>Operations that used to raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a> now raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>, since
<a class="reference internal" href="exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a> is now an alias of <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p>
</div>
<div class="section" id="text-i-o">
<h3>16.2.1.1. Text I/O<a class="headerlink" href="#text-i-o" title="永久链接至标题">¶</a></h3>
<p>Text I/O expects and produces <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> objects.  This means that whenever
the backing store is natively made of bytes (such as in the case of a file),
encoding and decoding of data is made transparently as well as optional
translation of platform-specific newline characters.</p>
<p>The easiest way to create a text stream is with <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-meth docutils literal notranslate"><span class="pre">open()</span></code></a>, optionally
specifying an encoding:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s2">&quot;myfile.txt&quot;</span><span class="p">,</span> <span class="s2">&quot;r&quot;</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s2">&quot;utf-8&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>In-memory text streams are also available as <a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code></a> objects:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">f</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">StringIO</span><span class="p">(</span><span class="s2">&quot;some initial text data&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>The text stream API is described in detail in the documentation of
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a>.</p>
</div>
<div class="section" id="binary-i-o">
<h3>16.2.1.2. Binary I/O<a class="headerlink" href="#binary-i-o" title="永久链接至标题">¶</a></h3>
<p>Binary I/O (also called <em>buffered I/O</em>) expects
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like objects</span></a> and produces <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>
objects.  No encoding, decoding, or newline translation is performed.  This
category of streams can be used for all kinds of non-text data, and also when
manual control over the handling of text data is desired.</p>
<p>The easiest way to create a binary stream is with <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-meth docutils literal notranslate"><span class="pre">open()</span></code></a> with <code class="docutils literal notranslate"><span class="pre">'b'</span></code> in
the mode string:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s2">&quot;myfile.jpg&quot;</span><span class="p">,</span> <span class="s2">&quot;rb&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>In-memory binary streams are also available as <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a> objects:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">f</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">BytesIO</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;some initial binary data: </span><span class="se">\x00\x01</span><span class="s2">&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>The binary stream API is described in detail in the docs of
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>.</p>
<p>Other library modules may provide additional ways to create text or binary
streams.  See <a class="reference internal" href="socket.html#socket.socket.makefile" title="socket.socket.makefile"><code class="xref py py-meth docutils literal notranslate"><span class="pre">socket.socket.makefile()</span></code></a> for example.</p>
</div>
<div class="section" id="raw-i-o">
<h3>16.2.1.3. Raw I/O<a class="headerlink" href="#raw-i-o" title="永久链接至标题">¶</a></h3>
<p>Raw I/O (also called <em>unbuffered I/O</em>) is generally used as a low-level
building-block for binary and text streams; it is rarely useful to directly
manipulate a raw stream from user code.  Nevertheless, you can create a raw
stream by opening a file in binary mode with buffering disabled:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">f</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="s2">&quot;myfile.jpg&quot;</span><span class="p">,</span> <span class="s2">&quot;rb&quot;</span><span class="p">,</span> <span class="n">buffering</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>
</pre></div>
</div>
<p>The raw stream API is described in detail in the docs of <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a>.</p>
</div>
</div>
<div class="section" id="high-level-module-interface">
<h2>16.2.2. High-level Module Interface<a class="headerlink" href="#high-level-module-interface" title="永久链接至标题">¶</a></h2>
<dl class="data">
<dt id="io.DEFAULT_BUFFER_SIZE">
<code class="descclassname">io.</code><code class="descname">DEFAULT_BUFFER_SIZE</code><a class="headerlink" href="#io.DEFAULT_BUFFER_SIZE" title="永久链接至目标">¶</a></dt>
<dd><p>An int containing the default buffer size used by the module's buffered I/O
classes.  <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> uses the file's blksize (as obtained by
<a class="reference internal" href="os.html#os.stat" title="os.stat"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.stat()</span></code></a>) if possible.</p>
</dd></dl>

<dl class="function">
<dt id="io.open">
<code class="descclassname">io.</code><code class="descname">open</code><span class="sig-paren">(</span><em>file</em>, <em>mode='r'</em>, <em>buffering=-1</em>, <em>encoding=None</em>, <em>errors=None</em>, <em>newline=None</em>, <em>closefd=True</em>, <em>opener=None</em><span class="sig-paren">)</span><a class="headerlink" href="#io.open" title="永久链接至目标">¶</a></dt>
<dd><p>This is an alias for the builtin <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function.</p>
</dd></dl>

<dl class="exception">
<dt id="io.BlockingIOError">
<em class="property">exception </em><code class="descclassname">io.</code><code class="descname">BlockingIOError</code><a class="headerlink" href="#io.BlockingIOError" title="永久链接至目标">¶</a></dt>
<dd><p>This is a compatibility alias for the builtin <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a>
exception.</p>
</dd></dl>

<dl class="exception">
<dt id="io.UnsupportedOperation">
<em class="property">exception </em><code class="descclassname">io.</code><code class="descname">UnsupportedOperation</code><a class="headerlink" href="#io.UnsupportedOperation" title="永久链接至目标">¶</a></dt>
<dd><p>An exception inheriting <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> and <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> that is raised
when an unsupported operation is called on a stream.</p>
</dd></dl>

<div class="section" id="in-memory-streams">
<h3>16.2.2.1. In-memory streams<a class="headerlink" href="#in-memory-streams" title="永久链接至标题">¶</a></h3>
<p>It is also possible to use a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> or <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> as a
file for both reading and writing.  For strings <a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code></a> can be used
like a file opened in text mode.  <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a> can be used like a file
opened in binary mode.  Both provide full read-write capabilities with random
access.</p>
<div class="admonition seealso">
<p class="first admonition-title">参见</p>
<dl class="last docutils">
<dt><a class="reference internal" href="sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a></dt>
<dd>contains the standard IO streams: <a class="reference internal" href="sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdin</span></code></a>, <a class="reference internal" href="sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdout</span></code></a>,
and <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stderr</span></code></a>.</dd>
</dl>
</div>
</div>
</div>
<div class="section" id="class-hierarchy">
<h2>16.2.3. Class hierarchy<a class="headerlink" href="#class-hierarchy" title="永久链接至标题">¶</a></h2>
<p>The implementation of I/O streams is organized as a hierarchy of classes.  First
<a class="reference internal" href="../glossary.html#term-abstract-base-class"><span class="xref std std-term">abstract base classes</span></a> (ABCs), which are used to
specify the various categories of streams, then concrete classes providing the
standard stream implementations.</p>
<blockquote>
<div><div class="admonition note">
<p class="first admonition-title">注解</p>
<p class="last">The abstract base classes also provide default implementations of some
methods in order to help implementation of concrete stream classes.  For
example, <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> provides unoptimized implementations of
<code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code> and <a class="reference internal" href="#io.IOBase.readline" title="io.IOBase.readline"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readline()</span></code></a>.</p>
</div>
</div></blockquote>
<p>At the top of the I/O hierarchy is the abstract base class <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>.  It
defines the basic interface to a stream.  Note, however, that there is no
separation between reading and writing to streams; implementations are allowed
to raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnsupportedOperation</span></code></a> if they do not support a given operation.</p>
<p>The <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> ABC extends <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>.  It deals with the reading
and writing of bytes to a stream.  <a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">FileIO</span></code></a> subclasses <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a>
to provide an interface to files in the machine's file system.</p>
<p>The <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> ABC deals with buffering on a raw byte stream
(<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a>).  Its subclasses, <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a>,
<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a>, and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRWPair</span></code></a> buffer streams that are
readable, writable, and both readable and writable.  <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code></a>
provides a buffered interface to random access streams.  Another
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> subclass, <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a>, is a stream of in-memory
bytes.</p>
<p>The <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> ABC, another subclass of <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>, deals with
streams whose bytes represent text, and handles encoding and decoding to and
from strings. <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code></a>, which extends it, is a buffered text
interface to a buffered raw stream (<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>). Finally,
<a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code></a> is an in-memory stream for text.</p>
<p>Argument names are not part of the specification, and only the arguments of
<a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> are intended to be used as keyword arguments.</p>
<p>The following table summarizes the ABCs provided by the <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module:</p>
<table border="1" class="docutils">
<colgroup>
<col width="21%" />
<col width="15%" />
<col width="21%" />
<col width="43%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">ABC</th>
<th class="head">Inherits</th>
<th class="head">Stub Methods</th>
<th class="head">Mixin Methods and Properties</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a></td>
<td>&#160;</td>
<td><code class="docutils literal notranslate"><span class="pre">fileno</span></code>, <code class="docutils literal notranslate"><span class="pre">seek</span></code>,
and <code class="docutils literal notranslate"><span class="pre">truncate</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">close</span></code>, <code class="docutils literal notranslate"><span class="pre">closed</span></code>, <code class="docutils literal notranslate"><span class="pre">__enter__</span></code>,
<code class="docutils literal notranslate"><span class="pre">__exit__</span></code>, <code class="docutils literal notranslate"><span class="pre">flush</span></code>, <code class="docutils literal notranslate"><span class="pre">isatty</span></code>, <code class="docutils literal notranslate"><span class="pre">__iter__</span></code>,
<code class="docutils literal notranslate"><span class="pre">__next__</span></code>, <code class="docutils literal notranslate"><span class="pre">readable</span></code>, <code class="docutils literal notranslate"><span class="pre">readline</span></code>,
<code class="docutils literal notranslate"><span class="pre">readlines</span></code>, <code class="docutils literal notranslate"><span class="pre">seekable</span></code>, <code class="docutils literal notranslate"><span class="pre">tell</span></code>,
<code class="docutils literal notranslate"><span class="pre">writable</span></code>, and <code class="docutils literal notranslate"><span class="pre">writelines</span></code></td>
</tr>
<tr class="row-odd"><td><a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a></td>
<td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a></td>
<td><code class="docutils literal notranslate"><span class="pre">readinto</span></code> and
<code class="docutils literal notranslate"><span class="pre">write</span></code></td>
<td>Inherited <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> methods, <code class="docutils literal notranslate"><span class="pre">read</span></code>,
and <code class="docutils literal notranslate"><span class="pre">readall</span></code></td>
</tr>
<tr class="row-even"><td><a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a></td>
<td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a></td>
<td><code class="docutils literal notranslate"><span class="pre">detach</span></code>, <code class="docutils literal notranslate"><span class="pre">read</span></code>,
<code class="docutils literal notranslate"><span class="pre">read1</span></code>, and <code class="docutils literal notranslate"><span class="pre">write</span></code></td>
<td>Inherited <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> methods, <code class="docutils literal notranslate"><span class="pre">readinto</span></code>,
and <code class="docutils literal notranslate"><span class="pre">readinto1</span></code></td>
</tr>
<tr class="row-odd"><td><a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a></td>
<td><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a></td>
<td><code class="docutils literal notranslate"><span class="pre">detach</span></code>, <code class="docutils literal notranslate"><span class="pre">read</span></code>,
<code class="docutils literal notranslate"><span class="pre">readline</span></code>, and
<code class="docutils literal notranslate"><span class="pre">write</span></code></td>
<td>Inherited <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> methods, <code class="docutils literal notranslate"><span class="pre">encoding</span></code>,
<code class="docutils literal notranslate"><span class="pre">errors</span></code>, and <code class="docutils literal notranslate"><span class="pre">newlines</span></code></td>
</tr>
</tbody>
</table>
<div class="section" id="i-o-base-classes">
<h3>16.2.3.1. I/O Base Classes<a class="headerlink" href="#i-o-base-classes" title="永久链接至标题">¶</a></h3>
<dl class="class">
<dt id="io.IOBase">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">IOBase</code><a class="headerlink" href="#io.IOBase" title="永久链接至目标">¶</a></dt>
<dd><p>The abstract base class for all I/O classes, acting on streams of bytes.
There is no public constructor.</p>
<p>This class provides empty abstract implementations for many methods
that derived classes can override selectively; the default
implementations represent a file that cannot be read, written or
seeked.</p>
<p>Even though <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> does not declare <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code>,
or <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code> because their signatures will vary, implementations and
clients should consider those methods part of the interface.  Also,
implementations may raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> (or <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnsupportedOperation</span></code></a>)
when operations they do not support are called.</p>
<p>The basic type used for binary data read from or written to a file is
<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.  Other <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like objects</span></a> are
accepted as method arguments too.  In some cases, such as
<a class="reference internal" href="#io.RawIOBase.readinto" title="io.RawIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a>, a writable object such as <a class="reference internal" href="stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a>
is required.  Text I/O classes work with <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> data.</p>
<p>Note that calling any method (even inquiries) on a closed stream is
undefined.  Implementations may raise <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> in this case.</p>
<p><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> (and its subclasses) supports the iterator protocol, meaning
that an <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> object can be iterated over yielding the lines in a
stream.  Lines are defined slightly differently depending on whether the
stream is a binary stream (yielding bytes), or a text stream (yielding
character strings).  See <a class="reference internal" href="#io.IOBase.readline" title="io.IOBase.readline"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readline()</span></code></a> below.</p>
<p><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> is also a context manager and therefore supports the
<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement.  In this example, <em>file</em> is closed after the
<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement's suite is finished---even if an exception occurs:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;spam.txt&#39;</span><span class="p">,</span> <span class="s1">&#39;w&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">file</span><span class="p">:</span>
    <span class="n">file</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s1">&#39;Spam and eggs!&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p><a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> provides these data attributes and methods:</p>
<dl class="method">
<dt id="io.IOBase.close">
<code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.close" title="永久链接至目标">¶</a></dt>
<dd><p>Flush and close this stream. This method has no effect if the file is
already closed. Once the file is closed, any operation on the file
(e.g. reading or writing) will raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>.</p>
<p>As a convenience, it is allowed to call this method more than once;
only the first call, however, will have an effect.</p>
</dd></dl>

<dl class="attribute">
<dt id="io.IOBase.closed">
<code class="descname">closed</code><a class="headerlink" href="#io.IOBase.closed" title="永久链接至目标">¶</a></dt>
<dd><p><code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream is closed.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.fileno">
<code class="descname">fileno</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.fileno" title="永久链接至目标">¶</a></dt>
<dd><p>Return the underlying file descriptor (an integer) of the stream if it
exists.  An <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> is raised if the IO object does not use a file
descriptor.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.flush">
<code class="descname">flush</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.flush" title="永久链接至目标">¶</a></dt>
<dd><p>Flush the write buffers of the stream if applicable.  This does nothing
for read-only and non-blocking streams.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.isatty">
<code class="descname">isatty</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.isatty" title="永久链接至目标">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream is interactive (i.e., connected to
a terminal/tty device).</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.readable">
<code class="descname">readable</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.readable" title="永久链接至目标">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream can be read from.  If <code class="docutils literal notranslate"><span class="pre">False</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code>
will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.readline">
<code class="descname">readline</code><span class="sig-paren">(</span><em>size=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.readline" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return one line from the stream.  If <em>size</em> is specified, at
most <em>size</em> bytes will be read.</p>
<p>The line terminator is always <code class="docutils literal notranslate"><span class="pre">b'\n'</span></code> for binary files; for text files,
the <em>newline</em> argument to <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> can be used to select the line
terminator(s) recognized.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.readlines">
<code class="descname">readlines</code><span class="sig-paren">(</span><em>hint=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.readlines" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return a list of lines from the stream.  <em>hint</em> can be specified
to control the number of lines read: no more lines will be read if the
total size (in bytes/characters) of all lines so far exceeds <em>hint</em>.</p>
<p>Note that it's already possible to iterate on file objects using <code class="docutils literal notranslate"><span class="pre">for</span>
<span class="pre">line</span> <span class="pre">in</span> <span class="pre">file:</span> <span class="pre">...</span></code> without calling <code class="docutils literal notranslate"><span class="pre">file.readlines()</span></code>.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.seek">
<code class="descname">seek</code><span class="sig-paren">(</span><em>offset</em><span class="optional">[</span>, <em>whence</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.seek" title="永久链接至目标">¶</a></dt>
<dd><p>Change the stream position to the given byte <em>offset</em>.  <em>offset</em> is
interpreted relative to the position indicated by <em>whence</em>.  The default
value for <em>whence</em> is <code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_SET</span></code>.  Values for <em>whence</em> are:</p>
<ul class="simple">
<li><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_SET</span></code> or <code class="docutils literal notranslate"><span class="pre">0</span></code> -- start of the stream (the default);
<em>offset</em> should be zero or positive</li>
<li><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_CUR</span></code> or <code class="docutils literal notranslate"><span class="pre">1</span></code> -- current stream position; <em>offset</em> may
be negative</li>
<li><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_END</span></code> or <code class="docutils literal notranslate"><span class="pre">2</span></code> -- end of the stream; <em>offset</em> is usually
negative</li>
</ul>
<p>Return the new absolute position.</p>
<div class="versionadded">
<p><span class="versionmodified">3.1 新版功能: </span>The <code class="docutils literal notranslate"><span class="pre">SEEK_*</span></code> constants.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">3.3 新版功能: </span>Some operating systems could support additional values, like
<code class="xref py py-data docutils literal notranslate"><span class="pre">os.SEEK_HOLE</span></code> or <code class="xref py py-data docutils literal notranslate"><span class="pre">os.SEEK_DATA</span></code>. The valid values
for a file could depend on it being open in text or binary mode.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.seekable">
<code class="descname">seekable</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.seekable" title="永久链接至目标">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream supports random access.  If <code class="docutils literal notranslate"><span class="pre">False</span></code>,
<a class="reference internal" href="#io.IOBase.seek" title="io.IOBase.seek"><code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code></a>, <a class="reference internal" href="#io.IOBase.tell" title="io.IOBase.tell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">tell()</span></code></a> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">truncate()</span></code></a> will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.tell">
<code class="descname">tell</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.tell" title="永久链接至目标">¶</a></dt>
<dd><p>Return the current stream position.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.truncate">
<code class="descname">truncate</code><span class="sig-paren">(</span><em>size=None</em><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.truncate" title="永久链接至目标">¶</a></dt>
<dd><p>Resize the stream to the given <em>size</em> in bytes (or the current position
if <em>size</em> is not specified).  The current stream position isn't changed.
This resizing can extend or reduce the current file size.  In case of
extension, the contents of the new file area depend on the platform
(on most systems, additional bytes are zero-filled).  The new file size
is returned.</p>
</dd></dl>

<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Windows will now zero-fill files when extending.</p>
</div>
<dl class="method">
<dt id="io.IOBase.writable">
<code class="descname">writable</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.writable" title="永久链接至目标">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the stream supports writing.  If <code class="docutils literal notranslate"><span class="pre">False</span></code>,
<code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">truncate()</span></code></a> will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.writelines">
<code class="descname">writelines</code><span class="sig-paren">(</span><em>lines</em><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.writelines" title="永久链接至目标">¶</a></dt>
<dd><p>Write a list of lines to the stream.  Line separators are not added, so it
is usual for each of the lines provided to have a line separator at the
end.</p>
</dd></dl>

<dl class="method">
<dt id="io.IOBase.__del__">
<code class="descname">__del__</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.IOBase.__del__" title="永久链接至目标">¶</a></dt>
<dd><p>Prepare for object destruction. <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> provides a default
implementation of this method that calls the instance's
<a class="reference internal" href="#io.IOBase.close" title="io.IOBase.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method.</p>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.RawIOBase">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">RawIOBase</code><a class="headerlink" href="#io.RawIOBase" title="永久链接至目标">¶</a></dt>
<dd><p>Base class for raw binary I/O.  It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>.  There is no
public constructor.</p>
<p>Raw binary I/O typically provides low-level access to an underlying OS
device or API, and does not try to encapsulate it in high-level primitives
(this is left to Buffered I/O and Text I/O, described later in this page).</p>
<p>In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>,
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> provides the following methods:</p>
<dl class="method">
<dt id="io.RawIOBase.read">
<code class="descname">read</code><span class="sig-paren">(</span><em>size=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#io.RawIOBase.read" title="永久链接至目标">¶</a></dt>
<dd><p>Read up to <em>size</em> bytes from the object and return them.  As a convenience,
if <em>size</em> is unspecified or -1, all bytes until EOF are returned.
Otherwise, only one system call is ever made.  Fewer than <em>size</em> bytes may
be returned if the operating system call returns fewer than <em>size</em> bytes.</p>
<p>If 0 bytes are returned, and <em>size</em> was not 0, this indicates end of file.
If the object is in non-blocking mode and no bytes are available,
<code class="docutils literal notranslate"><span class="pre">None</span></code> is returned.</p>
<p>The default implementation defers to <a class="reference internal" href="#io.RawIOBase.readall" title="io.RawIOBase.readall"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readall()</span></code></a> and
<a class="reference internal" href="#io.RawIOBase.readinto" title="io.RawIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="io.RawIOBase.readall">
<code class="descname">readall</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.RawIOBase.readall" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return all the bytes from the stream until EOF, using multiple
calls to the stream if necessary.</p>
</dd></dl>

<dl class="method">
<dt id="io.RawIOBase.readinto">
<code class="descname">readinto</code><span class="sig-paren">(</span><em>b</em><span class="sig-paren">)</span><a class="headerlink" href="#io.RawIOBase.readinto" title="永久链接至目标">¶</a></dt>
<dd><p>Read bytes into a pre-allocated, writable
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> <em>b</em>, and return the
number of bytes read.  If the object is in non-blocking mode and no bytes
are available, <code class="docutils literal notranslate"><span class="pre">None</span></code> is returned.</p>
</dd></dl>

<dl class="method">
<dt id="io.RawIOBase.write">
<code class="descname">write</code><span class="sig-paren">(</span><em>b</em><span class="sig-paren">)</span><a class="headerlink" href="#io.RawIOBase.write" title="永久链接至目标">¶</a></dt>
<dd><p>Write the given <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>, <em>b</em>, to the
underlying raw stream, and return the number of
bytes written.  This can be less than the length of <em>b</em> in
bytes, depending on specifics of the underlying raw
stream, and especially if it is in non-blocking mode.  <code class="docutils literal notranslate"><span class="pre">None</span></code> is
returned if the raw stream is set not to block and no single byte could
be readily written to it.  The caller may release or mutate <em>b</em> after
this method returns, so the implementation should only access <em>b</em>
during the method call.</p>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.BufferedIOBase">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">BufferedIOBase</code><a class="headerlink" href="#io.BufferedIOBase" title="永久链接至目标">¶</a></dt>
<dd><p>Base class for binary streams that support some kind of buffering.
It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>. There is no public constructor.</p>
<p>The main difference with <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> is that methods <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a>,
<a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a> and <a class="reference internal" href="#io.BufferedIOBase.write" title="io.BufferedIOBase.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a> will try (respectively) to read as much
input as requested or to consume all given output, at the expense of
making perhaps more than one system call.</p>
<p>In addition, those methods can raise <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> if the
underlying raw stream is in non-blocking mode and cannot take or give
enough data; unlike their <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> counterparts, they will
never return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<p>Besides, the <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> method does not have a default
implementation that defers to <a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a>.</p>
<p>A typical <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> implementation should not inherit from a
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> implementation, but wrap one, like
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a> and <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a> do.</p>
<p><a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> provides or overrides these methods and attribute in
addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>:</p>
<dl class="attribute">
<dt id="io.BufferedIOBase.raw">
<code class="descname">raw</code><a class="headerlink" href="#io.BufferedIOBase.raw" title="永久链接至目标">¶</a></dt>
<dd><p>The underlying raw stream (a <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> instance) that
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> deals with.  This is not part of the
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> API and may not exist on some implementations.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedIOBase.detach">
<code class="descname">detach</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedIOBase.detach" title="永久链接至目标">¶</a></dt>
<dd><p>Separate the underlying raw stream from the buffer and return it.</p>
<p>After the raw stream has been detached, the buffer is in an unusable
state.</p>
<p>Some buffers, like <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a>, do not have the concept of a single
raw stream to return from this method.  They raise
<a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnsupportedOperation</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">3.1 新版功能.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="io.BufferedIOBase.read">
<code class="descname">read</code><span class="sig-paren">(</span><em>size=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedIOBase.read" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return up to <em>size</em> bytes.  If the argument is omitted, <code class="docutils literal notranslate"><span class="pre">None</span></code>,
or negative, data is read and returned until EOF is reached.  An empty
<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> object is returned if the stream is already at EOF.</p>
<p>If the argument is positive, and the underlying raw stream is not
interactive, multiple raw reads may be issued to satisfy the byte count
(unless EOF is reached first).  But for interactive raw streams, at most
one raw read will be issued, and a short result does not imply that EOF is
imminent.</p>
<p>A <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> is raised if the underlying raw stream is in
non blocking-mode, and has no data available at the moment.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedIOBase.read1">
<code class="descname">read1</code><span class="sig-paren">(</span><em>size=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedIOBase.read1" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return up to <em>size</em> bytes, with at most one call to the
underlying raw stream's <a class="reference internal" href="#io.RawIOBase.read" title="io.RawIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> (or
<a class="reference internal" href="#io.RawIOBase.readinto" title="io.RawIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a>) method.  This can be useful if you are
implementing your own buffering on top of a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>
object.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedIOBase.readinto">
<code class="descname">readinto</code><span class="sig-paren">(</span><em>b</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedIOBase.readinto" title="永久链接至目标">¶</a></dt>
<dd><p>Read bytes into a pre-allocated, writable
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> <em>b</em> and return the number of bytes read.</p>
<p>Like <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a>, multiple reads may be issued to the underlying raw
stream, unless the latter is interactive.</p>
<p>A <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> is raised if the underlying raw stream is in non
blocking-mode, and has no data available at the moment.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedIOBase.readinto1">
<code class="descname">readinto1</code><span class="sig-paren">(</span><em>b</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedIOBase.readinto1" title="永久链接至目标">¶</a></dt>
<dd><p>Read bytes into a pre-allocated, writable
<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> <em>b</em>, using at most one call to
the underlying raw stream's <a class="reference internal" href="#io.RawIOBase.read" title="io.RawIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> (or
<a class="reference internal" href="#io.RawIOBase.readinto" title="io.RawIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a>) method. Return the number of bytes read.</p>
<p>A <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> is raised if the underlying raw stream is in non
blocking-mode, and has no data available at the moment.</p>
<div class="versionadded">
<p><span class="versionmodified">3.5 新版功能.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="io.BufferedIOBase.write">
<code class="descname">write</code><span class="sig-paren">(</span><em>b</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedIOBase.write" title="永久链接至目标">¶</a></dt>
<dd><p>Write the given <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>, <em>b</em>, and return the number
of bytes written (always equal to the length of <em>b</em> in bytes, since if
the write fails an <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> will be raised).  Depending on the
actual implementation, these bytes may be readily written to the
underlying stream, or held in a buffer for performance and latency
reasons.</p>
<p>When in non-blocking mode, a <a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> is raised if the
data needed to be written to the raw stream but it couldn't accept
all the data without blocking.</p>
<p>The caller may release or mutate <em>b</em> after this method returns,
so the implementation should only access <em>b</em> during the method call.</p>
</dd></dl>

</dd></dl>

</div>
<div class="section" id="raw-file-i-o">
<h3>16.2.3.2. Raw File I/O<a class="headerlink" href="#raw-file-i-o" title="永久链接至标题">¶</a></h3>
<dl class="class">
<dt id="io.FileIO">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">FileIO</code><span class="sig-paren">(</span><em>name</em>, <em>mode='r'</em>, <em>closefd=True</em>, <em>opener=None</em><span class="sig-paren">)</span><a class="headerlink" href="#io.FileIO" title="永久链接至目标">¶</a></dt>
<dd><p><a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">FileIO</span></code></a> represents an OS-level file containing bytes data.
It implements the <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> interface (and therefore the
<a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> interface, too).</p>
<p>The <em>name</em> can be one of two things:</p>
<ul class="simple">
<li>a character string or <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> object representing the path to the
file which will be opened. In this case closefd must be <code class="docutils literal notranslate"><span class="pre">True</span></code> (the default)
otherwise an error will be raised.</li>
<li>an integer representing the number of an existing OS-level file descriptor
to which the resulting <a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">FileIO</span></code></a> object will give access. When the
FileIO object is closed this fd will be closed as well, unless <em>closefd</em>
is set to <code class="docutils literal notranslate"><span class="pre">False</span></code>.</li>
</ul>
<p>The <em>mode</em> can be <code class="docutils literal notranslate"><span class="pre">'r'</span></code>, <code class="docutils literal notranslate"><span class="pre">'w'</span></code>, <code class="docutils literal notranslate"><span class="pre">'x'</span></code> or <code class="docutils literal notranslate"><span class="pre">'a'</span></code> for reading
(default), writing, exclusive creation or appending. The file will be
created if it doesn't exist when opened for writing or appending; it will be
truncated when opened for writing. <a class="reference internal" href="exceptions.html#FileExistsError" title="FileExistsError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">FileExistsError</span></code></a> will be raised if
it already exists when opened for creating. Opening a file for creating
implies writing, so this mode behaves in a similar way to <code class="docutils literal notranslate"><span class="pre">'w'</span></code>. Add a
<code class="docutils literal notranslate"><span class="pre">'+'</span></code> to the mode to allow simultaneous reading and writing.</p>
<p>The <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code> (when called with a positive argument), <code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code>
and <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code> methods on this class will only make one system call.</p>
<p>A custom opener can be used by passing a callable as <em>opener</em>. The underlying
file descriptor for the file object is then obtained by calling <em>opener</em> with
(<em>name</em>, <em>flags</em>). <em>opener</em> must return an open file descriptor (passing
<a class="reference internal" href="os.html#os.open" title="os.open"><code class="xref py py-mod docutils literal notranslate"><span class="pre">os.open</span></code></a> as <em>opener</em> results in functionality similar to passing
<code class="docutils literal notranslate"><span class="pre">None</span></code>).</p>
<p>The newly created file is <a class="reference internal" href="os.html#fd-inheritance"><span class="std std-ref">non-inheritable</span></a>.</p>
<p>See the <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> built-in function for examples on using the <em>opener</em>
parameter.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The <em>opener</em> parameter was added.
The <code class="docutils literal notranslate"><span class="pre">'x'</span></code> mode was added.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.4 版更改: </span>The file is now non-inheritable.</p>
</div>
<p>In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a> and
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a>, <a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">FileIO</span></code></a> provides the following data
attributes:</p>
<dl class="attribute">
<dt id="io.FileIO.mode">
<code class="descname">mode</code><a class="headerlink" href="#io.FileIO.mode" title="永久链接至目标">¶</a></dt>
<dd><p>The mode as given in the constructor.</p>
</dd></dl>

<dl class="attribute">
<dt id="io.FileIO.name">
<code class="descname">name</code><a class="headerlink" href="#io.FileIO.name" title="永久链接至目标">¶</a></dt>
<dd><p>The file name.  This is the file descriptor of the file when no name is
given in the constructor.</p>
</dd></dl>

</dd></dl>

</div>
<div class="section" id="buffered-streams">
<h3>16.2.3.3. Buffered Streams<a class="headerlink" href="#buffered-streams" title="永久链接至标题">¶</a></h3>
<p>Buffered I/O streams provide a higher-level interface to an I/O device
than raw I/O does.</p>
<dl class="class">
<dt id="io.BytesIO">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">BytesIO</code><span class="sig-paren">(</span><span class="optional">[</span><em>initial_bytes</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BytesIO" title="永久链接至目标">¶</a></dt>
<dd><p>A stream implementation using an in-memory bytes buffer.  It inherits
<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>.  The buffer is discarded when the
<a class="reference internal" href="#io.IOBase.close" title="io.IOBase.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method is called.</p>
<p>The optional argument <em>initial_bytes</em> is a <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> that
contains initial data.</p>
<p><a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a> provides or overrides these methods in addition to those
from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>:</p>
<dl class="method">
<dt id="io.BytesIO.getbuffer">
<code class="descname">getbuffer</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BytesIO.getbuffer" title="永久链接至目标">¶</a></dt>
<dd><p>Return a readable and writable view over the contents of the buffer
without copying them.  Also, mutating the view will transparently
update the contents of the buffer:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">b</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">BytesIO</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;abcdef&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">view</span> <span class="o">=</span> <span class="n">b</span><span class="o">.</span><span class="n">getbuffer</span><span class="p">()</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">view</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">]</span> <span class="o">=</span> <span class="sa">b</span><span class="s2">&quot;56&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">b</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>
<span class="go">b&#39;ab56ef&#39;</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">注解</p>
<p class="last">As long as the view exists, the <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a> object cannot be
resized or closed.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">3.2 新版功能.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="io.BytesIO.getvalue">
<code class="descname">getvalue</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BytesIO.getvalue" title="永久链接至目标">¶</a></dt>
<dd><p>Return <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> containing the entire contents of the buffer.</p>
</dd></dl>

<dl class="method">
<dt id="io.BytesIO.read1">
<code class="descname">read1</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BytesIO.read1" title="永久链接至目标">¶</a></dt>
<dd><p>In <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a>, this is the same as <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code>.</p>
</dd></dl>

<dl class="method">
<dt id="io.BytesIO.readinto1">
<code class="descname">readinto1</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BytesIO.readinto1" title="永久链接至目标">¶</a></dt>
<dd><p>In <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a>, this is the same as <code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code>.</p>
<div class="versionadded">
<p><span class="versionmodified">3.5 新版功能.</span></p>
</div>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.BufferedReader">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">BufferedReader</code><span class="sig-paren">(</span><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedReader" title="永久链接至目标">¶</a></dt>
<dd><p>A buffer providing higher-level access to a readable, sequential
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> object.  It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>.
When reading data from this object, a larger amount of data may be
requested from the underlying raw stream, and kept in an internal buffer.
The buffered data can then be returned directly on subsequent reads.</p>
<p>The constructor creates a <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a> for the given readable
<em>raw</em> stream and <em>buffer_size</em>.  If <em>buffer_size</em> is omitted,
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal notranslate"><span class="pre">DEFAULT_BUFFER_SIZE</span></code></a> is used.</p>
<p><a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a> provides or overrides these methods in addition to
those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>:</p>
<dl class="method">
<dt id="io.BufferedReader.peek">
<code class="descname">peek</code><span class="sig-paren">(</span><span class="optional">[</span><em>size</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedReader.peek" title="永久链接至目标">¶</a></dt>
<dd><p>Return bytes from the stream without advancing the position.  At most one
single read on the raw stream is done to satisfy the call. The number of
bytes returned may be less or more than requested.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedReader.read">
<code class="descname">read</code><span class="sig-paren">(</span><span class="optional">[</span><em>size</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedReader.read" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return <em>size</em> bytes, or if <em>size</em> is not given or negative, until
EOF or if the read call would block in non-blocking mode.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedReader.read1">
<code class="descname">read1</code><span class="sig-paren">(</span><em>size</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedReader.read1" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return up to <em>size</em> bytes with only one call on the raw stream.
If at least one byte is buffered, only buffered bytes are returned.
Otherwise, one raw stream read call is made.</p>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.BufferedWriter">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">BufferedWriter</code><span class="sig-paren">(</span><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedWriter" title="永久链接至目标">¶</a></dt>
<dd><p>A buffer providing higher-level access to a writeable, sequential
<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> object.  It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>.
When writing to this object, data is normally placed into an internal
buffer.  The buffer will be written out to the underlying <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a>
object under various conditions, including:</p>
<ul class="simple">
<li>when the buffer gets too small for all pending data;</li>
<li>when <a class="reference internal" href="#io.BufferedWriter.flush" title="io.BufferedWriter.flush"><code class="xref py py-meth docutils literal notranslate"><span class="pre">flush()</span></code></a> is called;</li>
<li>when a <code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code> is requested (for <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code></a> objects);</li>
<li>when the <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a> object is closed or destroyed.</li>
</ul>
<p>The constructor creates a <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a> for the given writeable
<em>raw</em> stream.  If the <em>buffer_size</em> is not given, it defaults to
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal notranslate"><span class="pre">DEFAULT_BUFFER_SIZE</span></code></a>.</p>
<p><a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a> provides or overrides these methods in addition to
those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>:</p>
<dl class="method">
<dt id="io.BufferedWriter.flush">
<code class="descname">flush</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedWriter.flush" title="永久链接至目标">¶</a></dt>
<dd><p>Force bytes held in the buffer into the raw stream.  A
<a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> should be raised if the raw stream blocks.</p>
</dd></dl>

<dl class="method">
<dt id="io.BufferedWriter.write">
<code class="descname">write</code><span class="sig-paren">(</span><em>b</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedWriter.write" title="永久链接至目标">¶</a></dt>
<dd><p>Write the <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>, <em>b</em>, and return the
number of bytes written.  When in non-blocking mode, a
<a class="reference internal" href="exceptions.html#BlockingIOError" title="BlockingIOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BlockingIOError</span></code></a> is raised if the buffer needs to be written out but
the raw stream blocks.</p>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.BufferedRandom">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">BufferedRandom</code><span class="sig-paren">(</span><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedRandom" title="永久链接至目标">¶</a></dt>
<dd><p>A buffered interface to random access streams.  It inherits
<a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a> and <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a>, and further supports
<code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">tell()</span></code> functionality.</p>
<p>The constructor creates a reader and writer for a seekable raw stream, given
in the first argument.  If the <em>buffer_size</em> is omitted it defaults to
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal notranslate"><span class="pre">DEFAULT_BUFFER_SIZE</span></code></a>.</p>
<p><a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code></a> is capable of anything <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a> or
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a> can do.</p>
</dd></dl>

<dl class="class">
<dt id="io.BufferedRWPair">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">BufferedRWPair</code><span class="sig-paren">(</span><em>reader</em>, <em>writer</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><span class="sig-paren">)</span><a class="headerlink" href="#io.BufferedRWPair" title="永久链接至目标">¶</a></dt>
<dd><p>A buffered I/O object combining two unidirectional <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a>
objects -- one readable, the other writeable -- into a single bidirectional
endpoint.  It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>.</p>
<p><em>reader</em> and <em>writer</em> are <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">RawIOBase</span></code></a> objects that are readable and
writeable respectively.  If the <em>buffer_size</em> is omitted it defaults to
<a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><code class="xref py py-data docutils literal notranslate"><span class="pre">DEFAULT_BUFFER_SIZE</span></code></a>.</p>
<p><a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRWPair</span></code></a> implements all of <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a>'s methods
except for <a class="reference internal" href="#io.BufferedIOBase.detach" title="io.BufferedIOBase.detach"><code class="xref py py-meth docutils literal notranslate"><span class="pre">detach()</span></code></a>, which raises
<a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnsupportedOperation</span></code></a>.</p>
<div class="admonition warning">
<p class="first admonition-title">警告</p>
<p class="last"><a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRWPair</span></code></a> does not attempt to synchronize accesses to
its underlying raw streams.  You should not pass it the same object
as reader and writer; use <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code></a> instead.</p>
</div>
</dd></dl>

</div>
<div class="section" id="id1">
<h3>16.2.3.4. Text I/O<a class="headerlink" href="#id1" title="永久链接至标题">¶</a></h3>
<dl class="class">
<dt id="io.TextIOBase">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">TextIOBase</code><a class="headerlink" href="#io.TextIOBase" title="永久链接至目标">¶</a></dt>
<dd><p>Base class for text streams.  This class provides a character and line based
interface to stream I/O.  There is no <code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code> method because
Python's character strings are immutable.  It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>.
There is no public constructor.</p>
<p><a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> provides or overrides these data attributes and
methods in addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">IOBase</span></code></a>:</p>
<dl class="attribute">
<dt id="io.TextIOBase.encoding">
<code class="descname">encoding</code><a class="headerlink" href="#io.TextIOBase.encoding" title="永久链接至目标">¶</a></dt>
<dd><p>The name of the encoding used to decode the stream's bytes into
strings, and to encode strings into bytes.</p>
</dd></dl>

<dl class="attribute">
<dt id="io.TextIOBase.errors">
<code class="descname">errors</code><a class="headerlink" href="#io.TextIOBase.errors" title="永久链接至目标">¶</a></dt>
<dd><p>The error setting of the decoder or encoder.</p>
</dd></dl>

<dl class="attribute">
<dt id="io.TextIOBase.newlines">
<code class="descname">newlines</code><a class="headerlink" href="#io.TextIOBase.newlines" title="永久链接至目标">¶</a></dt>
<dd><p>A string, a tuple of strings, or <code class="docutils literal notranslate"><span class="pre">None</span></code>, indicating the newlines
translated so far.  Depending on the implementation and the initial
constructor flags, this may not be available.</p>
</dd></dl>

<dl class="attribute">
<dt id="io.TextIOBase.buffer">
<code class="descname">buffer</code><a class="headerlink" href="#io.TextIOBase.buffer" title="永久链接至目标">¶</a></dt>
<dd><p>The underlying binary buffer (a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> instance) that
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> deals with.  This is not part of the
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> API and may not exist in some implementations.</p>
</dd></dl>

<dl class="method">
<dt id="io.TextIOBase.detach">
<code class="descname">detach</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOBase.detach" title="永久链接至目标">¶</a></dt>
<dd><p>Separate the underlying binary buffer from the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> and
return it.</p>
<p>After the underlying buffer has been detached, the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> is
in an unusable state.</p>
<p>Some <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> implementations, like <a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code></a>, may not
have the concept of an underlying buffer and calling this method will
raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><code class="xref py py-exc docutils literal notranslate"><span class="pre">UnsupportedOperation</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">3.1 新版功能.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="io.TextIOBase.read">
<code class="descname">read</code><span class="sig-paren">(</span><em>size</em><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOBase.read" title="永久链接至目标">¶</a></dt>
<dd><p>Read and return at most <em>size</em> characters from the stream as a single
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>.  If <em>size</em> is negative or <code class="docutils literal notranslate"><span class="pre">None</span></code>, reads until EOF.</p>
</dd></dl>

<dl class="method">
<dt id="io.TextIOBase.readline">
<code class="descname">readline</code><span class="sig-paren">(</span><em>size=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOBase.readline" title="永久链接至目标">¶</a></dt>
<dd><p>Read until newline or EOF and return a single <code class="docutils literal notranslate"><span class="pre">str</span></code>.  If the stream is
already at EOF, an empty string is returned.</p>
<p>If <em>size</em> is specified, at most <em>size</em> characters will be read.</p>
</dd></dl>

<dl class="method">
<dt id="io.TextIOBase.seek">
<code class="descname">seek</code><span class="sig-paren">(</span><em>offset</em><span class="optional">[</span>, <em>whence</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOBase.seek" title="永久链接至目标">¶</a></dt>
<dd><p>Change the stream position to the given <em>offset</em>.  Behaviour depends on
the <em>whence</em> parameter.  The default value for <em>whence</em> is
<code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_SET</span></code>.</p>
<ul class="simple">
<li><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_SET</span></code> or <code class="docutils literal notranslate"><span class="pre">0</span></code>: seek from the start of the stream
(the default); <em>offset</em> must either be a number returned by
<a class="reference internal" href="#io.TextIOBase.tell" title="io.TextIOBase.tell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">TextIOBase.tell()</span></code></a>, or zero.  Any other <em>offset</em> value
produces undefined behaviour.</li>
<li><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_CUR</span></code> or <code class="docutils literal notranslate"><span class="pre">1</span></code>: &quot;seek&quot; to the current position;
<em>offset</em> must be zero, which is a no-operation (all other values
are unsupported).</li>
<li><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_END</span></code> or <code class="docutils literal notranslate"><span class="pre">2</span></code>: seek to the end of the stream;
<em>offset</em> must be zero (all other values are unsupported).</li>
</ul>
<p>Return the new absolute position as an opaque number.</p>
<div class="versionadded">
<p><span class="versionmodified">3.1 新版功能: </span>The <code class="docutils literal notranslate"><span class="pre">SEEK_*</span></code> constants.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="io.TextIOBase.tell">
<code class="descname">tell</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOBase.tell" title="永久链接至目标">¶</a></dt>
<dd><p>Return the current stream position as an opaque number.  The number
does not usually represent a number of bytes in the underlying
binary storage.</p>
</dd></dl>

<dl class="method">
<dt id="io.TextIOBase.write">
<code class="descname">write</code><span class="sig-paren">(</span><em>s</em><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOBase.write" title="永久链接至目标">¶</a></dt>
<dd><p>Write the string <em>s</em> to the stream and return the number of characters
written.</p>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.TextIOWrapper">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">TextIOWrapper</code><span class="sig-paren">(</span><em>buffer</em>, <em>encoding=None</em>, <em>errors=None</em>, <em>newline=None</em>, <em>line_buffering=False</em>, <em>write_through=False</em><span class="sig-paren">)</span><a class="headerlink" href="#io.TextIOWrapper" title="永久链接至目标">¶</a></dt>
<dd><p>A buffered text stream over a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedIOBase</span></code></a> binary stream.
It inherits <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a>.</p>
<p><em>encoding</em> gives the name of the encoding that the stream will be decoded or
encoded with.  It defaults to
<a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><code class="xref py py-func docutils literal notranslate"><span class="pre">locale.getpreferredencoding(False)</span></code></a>.</p>
<p><em>errors</em> is an optional string that specifies how encoding and decoding
errors are to be handled.  Pass <code class="docutils literal notranslate"><span class="pre">'strict'</span></code> to raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>
exception if there is an encoding error (the default of <code class="docutils literal notranslate"><span class="pre">None</span></code> has the same
effect), or pass <code class="docutils literal notranslate"><span class="pre">'ignore'</span></code> to ignore errors.  (Note that ignoring encoding
errors can lead to data loss.)  <code class="docutils literal notranslate"><span class="pre">'replace'</span></code> causes a replacement marker
(such as <code class="docutils literal notranslate"><span class="pre">'?'</span></code>) to be inserted where there is malformed data.
<code class="docutils literal notranslate"><span class="pre">'backslashreplace'</span></code> causes malformed data to be replaced by a
backslashed escape sequence.  When writing, <code class="docutils literal notranslate"><span class="pre">'xmlcharrefreplace'</span></code>
(replace with the appropriate XML character reference)  or <code class="docutils literal notranslate"><span class="pre">'namereplace'</span></code>
(replace with <code class="docutils literal notranslate"><span class="pre">\N{...}</span></code> escape sequences) can be used.  Any other error
handling name that has been registered with
<a class="reference internal" href="codecs.html#codecs.register_error" title="codecs.register_error"><code class="xref py py-func docutils literal notranslate"><span class="pre">codecs.register_error()</span></code></a> is also valid.</p>
<p id="index-1"><em>newline</em> controls how line endings are handled.  It can be <code class="docutils literal notranslate"><span class="pre">None</span></code>,
<code class="docutils literal notranslate"><span class="pre">''</span></code>, <code class="docutils literal notranslate"><span class="pre">'\n'</span></code>, <code class="docutils literal notranslate"><span class="pre">'\r'</span></code>, and <code class="docutils literal notranslate"><span class="pre">'\r\n'</span></code>.  It works as follows:</p>
<ul class="simple">
<li>When reading input from the stream, if <em>newline</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>,
<a class="reference internal" href="../glossary.html#term-universal-newlines"><span class="xref std std-term">universal newlines</span></a> mode is enabled.  Lines in the input can end in
<code class="docutils literal notranslate"><span class="pre">'\n'</span></code>, <code class="docutils literal notranslate"><span class="pre">'\r'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'\r\n'</span></code>, and these are translated into <code class="docutils literal notranslate"><span class="pre">'\n'</span></code>
before being returned to the caller.  If it is <code class="docutils literal notranslate"><span class="pre">''</span></code>, universal newlines
mode is enabled, but line endings are returned to the caller untranslated.
If it has any of the other legal values, input lines are only terminated
by the given string, and the line ending is returned to the caller
untranslated.</li>
<li>When writing output to the stream, if <em>newline</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, any <code class="docutils literal notranslate"><span class="pre">'\n'</span></code>
characters written are translated to the system default line separator,
<a class="reference internal" href="os.html#os.linesep" title="os.linesep"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.linesep</span></code></a>.  If <em>newline</em> is <code class="docutils literal notranslate"><span class="pre">''</span></code> or <code class="docutils literal notranslate"><span class="pre">'\n'</span></code>, no translation
takes place.  If <em>newline</em> is any of the other legal values, any <code class="docutils literal notranslate"><span class="pre">'\n'</span></code>
characters written are translated to the given string.</li>
</ul>
<p>If <em>line_buffering</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">flush()</span></code> is implied when a call to
write contains a newline character or a carriage return.</p>
<p>If <em>write_through</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>, calls to <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code> are guaranteed
not to be buffered: any data written on the <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code></a>
object is immediately handled to its underlying binary <em>buffer</em>.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The <em>write_through</em> argument has been added.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The default <em>encoding</em> is now <code class="docutils literal notranslate"><span class="pre">locale.getpreferredencoding(False)</span></code>
instead of <code class="docutils literal notranslate"><span class="pre">locale.getpreferredencoding()</span></code>. Don't change temporary the
locale encoding using <a class="reference internal" href="locale.html#locale.setlocale" title="locale.setlocale"><code class="xref py py-func docutils literal notranslate"><span class="pre">locale.setlocale()</span></code></a>, use the current locale
encoding instead of the user preferred encoding.</p>
</div>
<p><a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code></a> provides one attribute in addition to those of
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> and its parents:</p>
<dl class="attribute">
<dt id="io.TextIOWrapper.line_buffering">
<code class="descname">line_buffering</code><a class="headerlink" href="#io.TextIOWrapper.line_buffering" title="永久链接至目标">¶</a></dt>
<dd><p>Whether line buffering is enabled.</p>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="io.StringIO">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">StringIO</code><span class="sig-paren">(</span><em>initial_value=''</em>, <em>newline='\n'</em><span class="sig-paren">)</span><a class="headerlink" href="#io.StringIO" title="永久链接至目标">¶</a></dt>
<dd><p>An in-memory stream for text I/O.  The text buffer is discarded when the
<a class="reference internal" href="#io.IOBase.close" title="io.IOBase.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method is called.</p>
<p>The initial value of the buffer can be set by providing <em>initial_value</em>.
If newline translation is enabled, newlines will be encoded as if by
<a class="reference internal" href="#io.TextIOBase.write" title="io.TextIOBase.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a>.  The stream is positioned at the start of
the buffer.</p>
<p>The <em>newline</em> argument works like that of <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code></a>.
The default is to consider only <code class="docutils literal notranslate"><span class="pre">\n</span></code> characters as ends of lines and
to do no newline translation.  If <em>newline</em> is set to <code class="docutils literal notranslate"><span class="pre">None</span></code>,
newlines are written as <code class="docutils literal notranslate"><span class="pre">\n</span></code> on all platforms, but universal
newline decoding is still performed when reading.</p>
<p><a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code></a> provides this method in addition to those from
<a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOBase</span></code></a> and its parents:</p>
<dl class="method">
<dt id="io.StringIO.getvalue">
<code class="descname">getvalue</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#io.StringIO.getvalue" title="永久链接至目标">¶</a></dt>
<dd><p>Return a <code class="docutils literal notranslate"><span class="pre">str</span></code> containing the entire contents of the buffer.
Newlines are decoded as if by <a class="reference internal" href="#io.TextIOBase.read" title="io.TextIOBase.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a>, although
the stream position is not changed.</p>
</dd></dl>

<p>Example usage:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">io</span>

<span class="n">output</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">StringIO</span><span class="p">()</span>
<span class="n">output</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s1">&#39;First line.</span><span class="se">\n</span><span class="s1">&#39;</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Second line.&#39;</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">output</span><span class="p">)</span>

<span class="c1"># Retrieve file contents -- this will be</span>
<span class="c1"># &#39;First line.\nSecond line.\n&#39;</span>
<span class="n">contents</span> <span class="o">=</span> <span class="n">output</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>

<span class="c1"># Close object and discard memory buffer --</span>
<span class="c1"># .getvalue() will now raise an exception.</span>
<span class="n">output</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</dd></dl>

<span class="target" id="index-2"></span><dl class="class">
<dt id="io.IncrementalNewlineDecoder">
<em class="property">class </em><code class="descclassname">io.</code><code class="descname">IncrementalNewlineDecoder</code><a class="headerlink" href="#io.IncrementalNewlineDecoder" title="永久链接至目标">¶</a></dt>
<dd><p>A helper codec that decodes newlines for <a class="reference internal" href="../glossary.html#term-universal-newlines"><span class="xref std std-term">universal newlines</span></a> mode.
It inherits <a class="reference internal" href="codecs.html#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><code class="xref py py-class docutils literal notranslate"><span class="pre">codecs.IncrementalDecoder</span></code></a>.</p>
</dd></dl>

</div>
</div>
<div class="section" id="performance">
<h2>16.2.4. Performance<a class="headerlink" href="#performance" title="永久链接至标题">¶</a></h2>
<p>This section discusses the performance of the provided concrete I/O
implementations.</p>
<div class="section" id="id2">
<h3>16.2.4.1. Binary I/O<a class="headerlink" href="#id2" title="永久链接至标题">¶</a></h3>
<p>By reading and writing only large chunks of data even when the user asks for a
single byte, buffered I/O hides any inefficiency in calling and executing the
operating system's unbuffered I/O routines.  The gain depends on the OS and the
kind of I/O which is performed.  For example, on some modern OSes such as Linux,
unbuffered disk I/O can be as fast as buffered I/O.  The bottom line, however,
is that buffered I/O offers predictable performance regardless of the platform
and the backing device.  Therefore, it is almost always preferable to use
buffered I/O rather than unbuffered I/O for binary data.</p>
</div>
<div class="section" id="id3">
<h3>16.2.4.2. Text I/O<a class="headerlink" href="#id3" title="永久链接至标题">¶</a></h3>
<p>Text I/O over a binary storage (such as a file) is significantly slower than
binary I/O over the same storage, because it requires conversions between
unicode and binary data using a character codec.  This can become noticeable
handling huge amounts of text data like large log files.  Also,
<code class="xref py py-meth docutils literal notranslate"><span class="pre">TextIOWrapper.tell()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">TextIOWrapper.seek()</span></code> are both quite slow
due to the reconstruction algorithm used.</p>
<p><a class="reference internal" href="#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">StringIO</span></code></a>, however, is a native in-memory unicode container and will
exhibit similar speed to <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">BytesIO</span></code></a>.</p>
</div>
<div class="section" id="multi-threading">
<h3>16.2.4.3. Multi-threading<a class="headerlink" href="#multi-threading" title="永久链接至标题">¶</a></h3>
<p><a class="reference internal" href="#io.FileIO" title="io.FileIO"><code class="xref py py-class docutils literal notranslate"><span class="pre">FileIO</span></code></a> objects are thread-safe to the extent that the operating system
calls (such as <code class="docutils literal notranslate"><span class="pre">read(2)</span></code> under Unix) they wrap are thread-safe too.</p>
<p>Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a>,
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRWPair</span></code></a>)
protect their internal structures using a lock; it is therefore safe to call
them from multiple threads at once.</p>
<p><a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code></a> objects are not thread-safe.</p>
</div>
<div class="section" id="reentrancy">
<h3>16.2.4.4. Reentrancy<a class="headerlink" href="#reentrancy" title="永久链接至标题">¶</a></h3>
<p>Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedReader</span></code></a>,
<a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedWriter</span></code></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRandom</span></code></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedRWPair</span></code></a>)
are not reentrant.  While reentrant calls will not happen in normal situations,
they can arise from doing I/O in a <a class="reference internal" href="signal.html#module-signal" title="signal: Set handlers for asynchronous events."><code class="xref py py-mod docutils literal notranslate"><span class="pre">signal</span></code></a> handler.  If a thread tries to
re-enter a buffered object which it is already accessing, a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a>
is raised.  Note this doesn't prohibit a different thread from entering the
buffered object.</p>
<p>The above implicitly extends to text files, since the <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function
will wrap a buffered object inside a <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">TextIOWrapper</span></code></a>.  This includes
standard streams and therefore affects the built-in function <a class="reference internal" href="functions.html#print" title="print"><code class="xref py py-func docutils literal notranslate"><span class="pre">print()</span></code></a> as
well.</p>
</div>
</div>
</div>


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  <h3><a href="../contents.html">內容目录</a></h3>
  <ul>
<li><a class="reference internal" href="#">16.2. <code class="docutils literal notranslate"><span class="pre">io</span></code> --- Core tools for working with streams</a><ul>
<li><a class="reference internal" href="#overview">16.2.1. Overview</a><ul>
<li><a class="reference internal" href="#text-i-o">16.2.1.1. Text I/O</a></li>
<li><a class="reference internal" href="#binary-i-o">16.2.1.2. Binary I/O</a></li>
<li><a class="reference internal" href="#raw-i-o">16.2.1.3. Raw I/O</a></li>
</ul>
</li>
<li><a class="reference internal" href="#high-level-module-interface">16.2.2. High-level Module Interface</a><ul>
<li><a class="reference internal" href="#in-memory-streams">16.2.2.1. In-memory streams</a></li>
</ul>
</li>
<li><a class="reference internal" href="#class-hierarchy">16.2.3. Class hierarchy</a><ul>
<li><a class="reference internal" href="#i-o-base-classes">16.2.3.1. I/O Base Classes</a></li>
<li><a class="reference internal" href="#raw-file-i-o">16.2.3.2. Raw File I/O</a></li>
<li><a class="reference internal" href="#buffered-streams">16.2.3.3. Buffered Streams</a></li>
<li><a class="reference internal" href="#id1">16.2.3.4. Text I/O</a></li>
</ul>
</li>
<li><a class="reference internal" href="#performance">16.2.4. Performance</a><ul>
<li><a class="reference internal" href="#id2">16.2.4.1. Binary I/O</a></li>
<li><a class="reference internal" href="#id3">16.2.4.2. Text I/O</a></li>
<li><a class="reference internal" href="#multi-threading">16.2.4.3. Multi-threading</a></li>
<li><a class="reference internal" href="#reentrancy">16.2.4.4. Reentrancy</a></li>
</ul>
</li>
</ul>
</li>
</ul>

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